A tire device to estimate conditions of a tire is used in the related art (for example, Patent Literature 1). According to the technique disclosed in Patent Literature 1, the tire device includes an acceleration sensor disposed at a tread of a tire (a portion of the tire that comes into contact with a road surface) inside the tire and detects a vibration generated in the tread portion from an output value of the acceleration sensor. The tire device estimates a coefficient of friction between the tire and the road surface from a time variation of a detected vibration level.
Also, besides a sensor used to estimate tire conditions, such as the acceleration sensor, the tire device generally includes a microcomputer and a transmitter inside the tire. Hence, the tire device processes data detected by the sensor and sends data to a device outside the tire. The tire device therefore requires power to drive the microcomputer and the transmitter and includes a battery cell inside the tire due to a difficulty of supplying power to the transmitter and the like inside the tire from a power supply (for example, a car battery) outside the tire.